Microphonic electron tube



J. ROTHSTEIN MICROPHONIC ELECTRON TUBE Nov. 27, 1945.

Filed June 24, 1945 F Q. 0 a z m 4 F. 6 6 8 8 5 I 4 4 4 M C I ll 1 IIII- II a V/// M 1 w G a F 3 8 J 2 e A [Ill A C M 0 J El 2 INVENTOR JEROMEROTHSTEIN Patented Nev. 21, 1945 UNITED STATES (Granted under the act ofMarch 3, 1883, as amended Ap 28; 370 0. G. 757) 2 Claims.

The invention described herein may be manufactored and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to electron emission tubes, and more particularlyto such a tube including a diaphragm for controlor measurement purposes.

some objects of this invention are to provide a device sensitive tomechanical vibrations; to provide a microphone to detect faint sounds inwhich the microphone is its own amplifier tube; to provide a device formeasuring changes in barometric pressure, temperature, turbulentpressure, shock pressure, altitude, windpressure, or wind velocity; toprovide a device which can measure depth of submergence in a liquid; andto provide a device for measuring the elastic properties of solids.

, invention resides in the microphone and vacuum tube elements, ashereinafter are more particularly described in the specification andsought to be defined in the claims. The specification is accompanied bya drawing in which Figure l is a partially-sectioned elevation throughone form of my invention, using a flexible bellowsf Referring now morespecifically to Figure 1,

' the tube there shown comprises an envelope [2,

Figure 2 is a section through a modified form anode electrodes C, G, andA respectively, with linkage L mechanically connecting the flexibleenvelope portion F to one of the electrodes, preferably the grid G, insuch a manner that movement of the flexible portion F changes theinterelectrode spacing and consequently the amplification iactor of thetube.

having a cathode M, a grid 16, and an anode l8. Cathode I4 and anode l8are stationary, and are supported by conventional lead-ins 20 and 22.The cathode I4 is indirectly heated by means of a filament 24 havinglead-ins 26.

In accordance with the present invention, the grid [6 is movably mountedbetween the cathode l4 and the anode I8. For this purpose it issupported on wires 3!] which extend to a rigid diaphragm 32. In thepresent case there are four such wires, and the diaphragm is circular.The latter is carried by a sensitive, flexible, metal bellows 34, theinner end of which is secured to a metal ring 36, which in turn issealed to the edge of a large aperture in the glass envelope l2.

In other cases, it the tube envelope I2 is made of metal, the bellows 34or the ring 36 may be welded directly to the metal envelope. In rarecases the bellows may be made of tempered glass, and in such case may besealed directly toa glass tube envelope.

Electrical connection to the grid it may be made by means of a lead 38secured to the ring 36. This may be done when there is no need toinsulate the diaphragm 32 and the bellows 36 from the grid, but in othercases, when an insulated connection is wanted, the grid connection maybe arranged as described hereinafter in connection with Figures 2 and 3.

The arrangement of the electrodes will be clear from Figure 4, whichshows how the grid wire formation H is held within a grid frame it, thelatter being carried by the support wires 30 (only the left-hand ends ofwhich are shown in Figure 4). Figure 4. also shows how the cathode canit is provided with an oxide or other emissive surface lfi on one sidethereof, this being the side which faces the grid l6 and anode M. Itwill be understood that the cathode can M is an enclosed box-likestructure, which may be open at the bottom, or if closed will haveapertures for the filament lead-ins 26. The filament 26 may be of anydesired shape, and is received and housed within the cathode can it.

When any mechanical vibration, sound, pressure, or other means ofproducing a displacement is impressed on the diaphragm 32, a change ofposition results which is applied to the grid it by means of theconnections 30. This changes the cathode-to-grid spacing (and also thegridto-anode spacing) and so changes the amplification factor of thetube. The mechanical resonance frequency of the diaphragm system can bevaried by varying the mass of the diaphragm 32 and the stifiness of thebellows 33. The tube 'ployed as a barometer or manometer.

should be carefully shielded from all sources of vibration other thanthose impressed on the diaphragm 32.

Figure 2 differs in eliminating the flexible bellows and instead using acircular flexible diaphragm 40. This is welded at its periphery to ametal ring 42,which in turn is sealed to the edge of a large aperture inglass envelope 44. The grid 46 is supported by wires 48 which arebrought together at a glass bead 50, and this is secured to diaphragm 40at its mid-point 52. Electrical connection to grid 46 is obtained bymeans of a lead-in 54, which is made very flexible at 56 in order not tointerfere with vibration of grid 48.

The arrangement of Figure 3 is the same as that shown in Figure 2 exceptfor the inclusion of two additional grids, there being a "space chargegrid" 60, and a suppressor grid 62. These grids may be stationary, likeall of the other electrodes except the control grid 64.

The tubes disclosed herein may be used as microphones because pressurevariations caused by sound waves cause the diaphragm to vibrate, therebycyclically changing mu," the amplification factor. In respect to currentflowing in the plate circuit of the tube, a voltage e on the grid hasthe same effect as a voltage 148 on the plate. If 1. now changes to avalue of a, and a voltage e is onthe grid, the efiect in the platecircuit will be that of a voltage p'e or a net change of con. whereA,u.=[b'#. We will thus have current variations in the plate circuit tocorrespond to changes in pressure of the sound wave.

If a carrier frequency were impressed on the grid, instead of a constantbias, the sound wave will modulate the carrier frequency.

Inasmuch as the plate current varies with the pressure applied to thesensitive element or diaphragm, the tube may be calibrated and used toindicate static pressure, and thus may be em- Because air pressurevaries with the altitude above the surface of the earth, the tube may becalibrated directly as an altimeter. If the structure is reinforced, andmade rigid, it may be used as a piezometer, and, inasmuch as waterpressure varies directly as the depth at which the pressure is beingdetermined, the tube may be used as a depth meter for submarines orother devices.

An expansible temperature responsive element may be connected to thediaphragm with a heat insulating connection, thus utilizing theinvention to measure or record temperature. In some cases, thetemperature responsive element may be'a bulb of liquid connected througha pipe to a chamber enclosing the outside of the diaphragm so thatexpansion of the liquid when increased in temperature will replace thediaphragm.

The. tube may also be used to measure wind velocity because a dynamicpressure is developed in excess of the normal atmospheric pressure. Usedas the manometer in connection with a Pitot tube, it may be used as anairspeed meter, or as a flow meter for liquids. Turbulent pressurechanges, in a wind tunnel for example, may also be measured. Suitablerecording devices enable continuous records to be made over long periodsof time in all applications of my improved tube. One such usablerecording device makes photographic trace of a light spot reflected fromthe mirror of a galvanometer energized by the output I to measure thesame and so replace devices such as an optical lever. For example, theYoung's modulus for a given specimen is determined by finding the strainor fractional elongation produced by a given stress. If the movable partof my tube is connected by a taut wire to a fixed point of the specimen,the application of a stress will cause a small displacement. The platecurrent indicator can be calibrated in terms of displacement, and thuselastic properties can be de termined.

The tube may also be used to measure forces or weights of objects. Theforce or weight is caused to act on the movable part of the tube by ataut wire or other suitable connection thereby producing a displacement.The plate current indicator may then be calibrated in terms of force orweight.

It is believed that the construction and operation of my improvedmicrophonic electron tube, as well as the advantages thereof, will beapparent from the foregoing detailed description. The electron tube usedmay be of the metal or glass envelope type, and may have any number ofelectrodes, and may be a high vacuum or a gas-filled type. The flexibleportion of the envelope may be metal and may be secured to the rigidenvelope portion by welding if the latter is also made of metal, or by ametal-to-glass seal if the latter is made of glass. For certain specialpurposes the bellows may be made of glass so tempered as to ffordflexibility, though for most purposes the flcxible part of the envelopeis preferably made of metal. If made of glass,-the bellows may be sealeddirectly to, a glass envelope.

It will be apparent that while I have shown and described my inventionin several preferred forms, other changes and modifications may be madein the structures disclosedwithout departing from the spirit of theinvention, as sought to be defined in the following claims.

I claim:

1. An electron tube responsive to vibratory wave motion comprising arigid envelope having a relatively large circular aperture in the sidewall thereof, a flexible bellows sensitive to vibratory waves, havingone end sealed to the envelope at the aperture and having its outer end.closed by a wave sensitive diaphragm, cathode, grid, and anodeelectrodes of generally fiat configuration in said envelope, and meansmechanically connecting the aforesaid diaphragm to one of saidelectrodes to vibrate such electrode and move it physically closer toand further from the other electrodes, whereby vibration of thediaphragm correspondingly changes the inter-electrode spacing of theelectrodes and thereby changes the amplification factor of the tube.

2. An electron tube responsive to vibratory wave motion comprising arigid envelope having a relatively large circular aperture in the sidewall thereof, a longitudinal flexible bellows sensitive to vibratorywaves, having one end sealed to the envelope at the aperture and havingits outer end closed by a wave sensitive diaphragm, cathode, grid, andanode electrodes in said envelope, said cathode, grid, and anodeelectrodes being generally flat and disposed generally parallel to theaforesaid diaphragm, and means mechanically connecting the aforesaiddiaphragm to said grid, whereby vibration of the diaphragmcorrespondingly changes the inter-electrode spacing of the electrodes.

JEROME ROTHSTEIN.

